Transfer-matrix theory of surface spin-echo experiments with molecules
Transfer-matrix theory of surface spin-echo experiments with molecules
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DOI：
10.1103/physreva.101.062703
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发表时间：
2020-06-02
影响因子：
2.9
通讯作者：
Krems, R., V
中科院分区：
文献类型：
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作者：
Cantin, J. T.;Alexandrowicz, G.;Krems, R., V
He-3束自旋回波实验已被用来研究离子液体的表面形态，分子和原子的表面扩散，声子色散，相子色散和相变。然而，He-3原子与表面或其吸附物之间的相互作用通常是各向同性的和弱的。为了克服这些限制，人们可以在表面自旋回波实验中使用分子代替He-3。分子的自由度，如旋转，可以用来提供额外的洞察表面和它们的吸附物的行为。事实上，最近的实验已经表明，正氢可以用作对Cu（115）表面的取向敏感的探针[O. Godsi，G. Corem，Y. J. T.阿尔科比坎坦河V. Krems，M. F.索默斯，J.迈耶，G.- J. Kroes，T. Maniv和G. Alexandrowicz，Nat. Commun. 8，15357（2017）]。然而，分子提供的额外自由度也带来了理论上的挑战：大量的分子状态和内部状态之间的磁场诱导耦合。在这里，我们提出了一个完全量子力学的方法来模拟分子表面自旋回波实验，并连接实验信号的时间无关的分子表面散射矩阵的元素。我们提出了一个一维的转移矩阵方法，包括分子超精细自由度和帐户的空间分离的分子波包由于磁控制场。将该方法应用于正氢原子的情况，证明了计算的实验信号对散射矩阵元的敏感性，并与实验进行了初步比较。本文设置阶段贝叶斯优化，以确定散射矩阵元素的实验测量和一个框架，描述分子表面自旋回波实验研究动态表面。
He-3 beam spin-echo experiments have been used to study surface morphology, molecular and atomic surface diffusion, phonon dispersions, phason dispersions, and phase transitions of ionic liquids. However, the interactions between He-3 atoms and surfaces or their adsorbates are typically isotropic and weak. To overcome these limitations, one can use molecules instead of He-3 in surface spin-echo experiments. The molecular degrees of freedom, such as rotation, may be exploited to provide additional insight into surfaces and the behavior of their adsorbates. Indeed, a recent experiment has shown that orthohydrogen can be used as a probe that is sensitive to the orientation of a Cu(115) surface [O. Godsi, G. Corem, Y. Alkoby, J. T. Cantin, R. V. Krems, M. F. Somers, J. Meyer, G.-J. Kroes, T. Maniv, and G. Alexandrowicz, Nat. Commun. 8, 15357 (2017)]. However, the additional degrees of freedom offered by molecules also pose a theoretical challenge: a large manifold of molecular states and magnetic-field-induced couplings between internal states. Here, we present a fully quantum-mechanical approach to model molecular surface spin-echo experiments and connect the experimental signal to the elements of the time-independent molecule-surface scattering matrix. We present a one-dimensional transfer-matrix method that includes the molecular hyperfine degrees of freedom and accounts for the spatial separation of the molecular wave packets due to the magnetic control fields. We apply the method to the case of orthohydrogen, show that the calculated experimental signal is sensitive to the scattering matrix elements, and perform a preliminary comparison to experiment. This paper sets the stage for Bayesian optimization to determine the scattering matrix elements from experimental measurements and for a framework that describes molecular surface spin-echo experiments to study dynamic surfaces.